A copying machine which is one of image forming apparatuses is widely used. As is well known, there are various types of copying machines. An electrostatic type copying machine employing a dry process developing method is one of the most popular machines. In the copying machine of this type, an electrostatic latent image is formed on a photoconductive drum, and the electrostatic image is then developed by use of a developing material which is formed as a magnetic brush. The development of the latent image is generally carried out by a dry process developing apparatus which includes a cylindrical developing sleeve facing the photoconductive drum.
A plurality of stationary permanent magnets, which are installed inside the developing sleeve, hold the magnetic particles on a periphery of the sleeve by magnetic attraction. The magnetic particles held on the periphery of the developing sleeve are called the magnetic brush for the development of the latent image. The developing sleeve is rotationally driven with respect to the magnets. The magnetic particles attracted onto the periphery of the sleeve are conveyed through the rotation of the sleeve and brought in contact with the photoconductive drum through an opening of a housing which accommodates the developing sleeve and an apparatus for supplying the magnetic particles to the developing sleeve. Thereby, the latent image on the photoconductive drum is developed to be processed into an image of the magnetic particles. This image is frequently called a toner image. The toner image is transferred to a sheet of paper, which is then subjected to a fixing process.
On the other hand, the cleaning of the photoconductive drum is made by use of, for example, a cleaning apparatus in which a magnetic brush of the magnetic particles is formed on a cleaning sleeve, which is almost the same as the sleeve of the developing apparatus. That is, the magnetic brush formed on the sleeve of the cleaning apparatus is brought into contact with the periphery of the photoconductive drum through an opening of a housing which accommodates the cleaning sleeve and other elements.
The developing apparatus and the cleaning apparatus of the above type have a problem described below. The magnetic particles carried on the periphery of the developing sleeve which is in the rotational state are affected by various forces due to mucosity of air, centrifugal force and the like. Thereby, some magnetic particles attracted on the periphery of the sleeve are liable to be removed and scattered into the air. The scattered magnetic particles smear the developed image formed on the photoconductive drum and other peripheral elements. As a result, the quality of the image transferred onto the paper is degraded.
For this reason, various means for preventing the scattering of the magnetic particles are provided for the conventional dry process developing apparatus. For example, the Japanese Laid-Open Utility Model Application No. 95360/1984, or the U.S. Pat. No. 4,592,653 (the assignee of which is the same as the assignee of the present application) discloses a seal member of a fur brush type, which is located over the developing sleeve. The front ends of the fur brush are kept in contact with the periphery of the photoconductive drum in its axial direction. This fur brush is effective in preventing the scattering of the magnetic particles which leak from the intermediate portion of the developing sleeve. However, the fur brush cannot totally seal the scattering resulting from both sides of the developing sleeve in its axial direction.
To cope with this scattering, it is necessary to seal a gap between the ends of the developing sleeve and an inner wall of the housing as well as a gap between the ends of the photoconductive drum and the ends of the developing apparatus. As anticipated from the above description, to effectively prevent the scattering with respect to the photoconductive drum, a number of independent seal members must be provided. For this reason, the conventional scheme for preventing the scattering is expensive, and the operation of attaching the seals is complex and cumbersome.
The situation described above is the same as for the magnetic brush cleaning apparatus. The magnetic particles which fly from the magnetic brush formed on the cleaning sleeve are deposited on and smear the periphery of the photoconductive drum.
As is well known, the magnetic particles are mainly classified into a one-component magnetic toner and a two-component magnetic toner. The one-component magnetic toner has the property of magnetic material. On the other hand, the two-component toner is made up of toner particles and iron particles. The above problems are particularly prominent for the two-component magnetic toner.